Daclizumab (DAC) is a humanized IgG1 monoclonal antibody that binds to the alpha subunit (CD25 or Tac) of the human high-affinity interleukin-2 (IL-2) receptor, which is expressed on the surface of activated, but not resting, T- and B-lymphocytes. When bound to CD25 on the activated cells, DAC blocks the formation of the high affinity IL-2 receptor complex, thereby blocking IL-2-induced proliferation of the activated cells.
As measured in direct binding assays on PHA blasts, DAC binds to CD25 with an approximate binding affinity (KD) of 0.3 nM, and inhibits the proliferation of PHA blasts in a dose-dependent manner (Hakimi et al., 1993, J. Immunol. 151(2):1075-85). At a suboptimal dose of IL-2 (2.5 ng/mL), 15 nM DAC inhibits proliferation of IL-2-dependent cell line Kit225/K6 by 50% (Pilson et al., 1997, J. Immunol. 159(3):1543-56). In an IL2-dependent antigen-induced T-cell proliferation assay, 50% inhibition of proliferation was observed with DAC in the range of 0.5-1 μg/mL (3-7 nM) (Junghans et al., 1990, Cancer Res. 50(5):1495-1502).
A version of DAC was previously marketed for the treatment of acute allograft rejection in renal transplant patients as an adjunct to an immunosuppressive regimen that includes cyclosporine and corticosteroids by Hoffman-La Roche, Inc. under the tradename ZENAPAX™. ZENAPAX™ was supplied as a concentrate for further dilution and intravenous administration. Each vial of concentrate contained 5 mL of a solution containing 5 mg/mL DAC, 3.6 mg/mL sodium phosphate monobasic monohydrate, 11 mg/mL sodium phosphate dibasic heptahydrate, 4.6 mg/mL sodium chloride, 0.2 mg/mL polysorbate 80 and HCl and/or NaOH sufficient to adjust the pH to pH 6.9. The recommended dose for both adult and pediatric patients was 1.0 mg/kg, prepared by diluting the calculated volume of 25 mg/5 mL ZENAPAX™ concentrate with 50 mL sterile 0.9% sodium chloride solution and administering intravenously via a peripheral or central vein over a 15-minute period.
DAC has also shown efficacy in the treatment of uveitis (Nussenblatt et al., 2004, FOCIS 2004 meeting; July 18-23, Montreal, QC. Abstract 4688; Nussenblatt et al., 2003, J. Autoimmun. 21:283-93) and multiple sclerosis (see, e.g., Bielekova et al., 2004, Proc. Nat'l. Acad. Sci. USA 101(23):8705-8708; Rose et al., 2007, Neurology 69:785-789; U.S. Pat. No. 7,258,859), and is currently the subject of ongoing clinical trials for the treatment of relapsing forms of multiple sclerosis. Currently, there are few, if any, treatments available for progressive forms of multiple sclerosis. The availability of such treatments would be desirable.